Cooling systems for underground transformers



Sept. 6, 1966 M. G. LEONARD 3,271,710

COOLING SYSTEMS FOR UNDERGROUND TRANSFORMERS Filed March 6, 1964 2Sheets-Sheet 1 Fig.2. 24 3 Fig.4. 5

28 26 4O,\\ 26 Q 6 42 L42 WITNESSES: i L Fi 3 INVENTOR ,hj KW) Merrill0. Leonard QW 0131M KW ATTORNEY P 6, 1966 M. G. LEONARD 3,271,710

COOLING SYSTEMS FOR UNDERGROUND TRANSFORMERS Filed March 6, 1964 2Sheets-Sheet 2 Fig. 6.

MAXIMUM RATED 8O 5O l0O- lE M P I::RATURE RISE 90? so 8O WINDING] ,J 2'4 L; 50 I m w 40 2 I} u 0 2 4 s 8 IO I2 [4 1e |e2o2224 HOURS 2 3 DAYST|ME- United States Patent 3,271,710 COOLING SYSTEMS FOR UNDERGROUNDTRANSFORMERS Merrill G. Leonard, Brookfield Township, Ohio, assignor toWestinghouse Electric Corporation, East Pittsburgh,

Pa., a corporation of Pennsylvania Filed Mar. 6, 1964, Ser. No. 349,8956 Claims. (Cl. 336-55) This invention relates in general to improvementsin the ventilation and safety of electrical inductive apparatus, andmore particularly to improvements in ventilation and safety relative totransformers mounted partially or wholly below ground level.

Some underground enclosures or vaults for housing transformers may havesolid covers for safety purposes, with the transformers beingsubstantially derated because of the lack of ventilation. Otherunderground vaults may have flat expanded metal covers, with some of theopenings in the expanded grill work being utilized for intake air andother openings being utilized to discharge heated air. The opposite airflow pattern set up by the expanded metal type cover results inconsiderable recirculation of the air, with the heated air immediatelyre-entering the transformer enclosure, with a resultant loss of coolingefiiciency. Further, the openings in the expanded metal cover arehazardous from a safety standpoint as it is easy for children to pushsticks and other foreign objects through the openings.

Accordingly, it is an object of this invention to provide a safe andefficient cooling system for inductive apparatus.

Another object of this invention is to provide a cooling system forunderground vault-mounted transformers that vw'll allow the transformersto be operated without reduction in rating.

A further object of the invention is to provide a cooling system forunderground vault-mounted transformers that substantially eliminatesrecirculation of the cooling air.

Another object of the invention is to provide a strong chimney effectwhich increases circulation of air around vault-mounted transformers.

A further object of this invention is to provide a transformer-electriclight pole combination which is safe, highly efficient, and whichprotects the transformer from damage when vehicles accidentally strikethe light pole.

Briefly, the present invention accomplishes the abovecited objects byproviding an enclosure disposed below ground level in which atransformer is mounted; said enclosure being provided with asubstantially domeshaped top having a fiat horizontal upper portion. Theinlet air enters near the bottom of the dome through long, thermallyinsulated ducts which discharge air near the bottom of the vault. Thelighter, heated air is discharged near the top of the dome. Thus, theintake and outlet air currents are separated not only by distance, butalso by height, substantially eliminating recirculation with itsresulting loss in cooling efficiency. The air inlet ducts prevent sticksand other foreign objects from being inserted into dangerous areas, andthe outlet ducts may be suitably baflled to prevent children frominserting foreign articles into dangerous areas.

Another embodiment of the invention is to mount a hollow polevor tubeover the top of the dome-shaped cover, such as an electric light pole.The hollow pole produces a strong chimney effect, greatly increasing aircirculation, and at the same time eliminating the necessity of airoutlets on the dome cover. Thus, there is absolutely no way for articlesto be inserted into the vault, except through the long intake ducts,which safely divert the articles away from any dangerous electricalpotentials.

Further objects and advantages of the invention will become apparent asthe following description proceeds and features of novelty whichcharacterize the invention will be pointed out in particularity in theclaims annexed to and forming a part of this specification.

For a better understanding of the invention, reference may be had to theaccompanying drawings, in which:

FIGURE 1 is a side elevation, partially in section, of an undergroundenclosure and transformer, illustrating one embodiment of the invention;

FIG. 2 is a top view of the apparatus shown in FIG. 1;

FIG. 3 is a side elevation, partially in section, of an undergroundvault and transformer combination illustrating another embodiment of theinvention;

FIG. 4 is a top view of the apparatus shown in FIG. 3;

FIG. 5 is a perspective view illustrating how the invention may becombined with electric street lighting apparatus to form a safe,efiicient, esthetically pleasing installation; and

FIG. 6 is a graph illustrating the winding and oil temperatures of avault-mounted transformer utilizing the teachings of this invention.

Referring now to the drawings, and FIG. 1 in particular, there is showna side elevation, partially in section, of a transformer-vaultinstallation 10, illustrating one embodiment of the invention. Inparticular, the transformer-vault installation 10 comprises an enclosureor vault 12, which may be constructed of concrete or other suitablematerial, and disposed "below the ground level 14. The bottom 16 of theenclosure 12 may consist of gravel to facilitate drainage, with atransformer 18 being disposed within the enclosure 12. Supports 29 maybe provided between the transformer 18 and the bottom 16, to insureadequate ventilation under the transformer. High voltage leads 13 and 15may enter the enclosure 12 from underground, and are connected to highvoltage bushings 17 and 19. Low voltage bushings 21, 23 and 25 haveleads 27, 29 and 31 connected respectively thereto, and may go out thesides of the enclosure 12 to serve connected loads, and may also extendtvertically, as will hereinafter be explained, to serve lighting loads.The transformer ground connection may be made through conductor 37 toterminal 33 on the transformer 18.

In order to prevent recirculation of cooling air which is caused by thepresence of adjacent opposite air flow patterns, a dome-like cover ortop 22 is provided and suitably attached to the enclosure 12 by nut andbolt combination 24, or other suitable fastening means. The cover 22 maybe constructed of steel, or other structurally strong materials. Thedome-shaped cover 22 allows a circulation of cooling air to be set uparound transformer 18, which takes full advantage of the natural laws ofcool and warm air flow, and prevents recirculation of the air whichlowers cooling efliciency. This is accomplished by providing one or moreopenings 26 around the bottom portion of cover 22, and one or moreopenings 28 around the upper or top portion of cover 22. The openings 26are for inlet air, and they are connected to ducts 30 which direct theinlet air towards the bottom of the enclosure 12. The ducts 30 should beformed of a ma terial having good thermal insulating properties, such asthe asbestos base materials, to prevent thermal blocks from being set upin the ducts which would prevent the desired air circulation. Theopenings 26 may be covered with a metallic grill work to prevent largeforeign objects from being placed in the ducts 30. Any objects, however,that are inserted into ducts 30, would be di verted from thetransformer, and thus the ducts 30 provide an additional safety factor.

As the incoming air, as shown by the arrows, is heated, it rises towardthe top of the dome cover 22. Air out lets 28 are provided to allow theheated air to readily escape the enclosure 22. The air discharge level,being substantially higher than the air intake level, prevents adjacentcontra air currents from setting up recirculation of the heated air backinto the enclosure 12. Further, a chimney effect is set up after a fewhours operation of the transformer 18, which provides a naturalcirculation, drawing fresh cooler air into the enclosure 12 throughinlet openings 26 and ducts 30, passing the air under, over and aroundthe transformer 18 and up to the air discharge outlets 28. The airdischarge outlets 28 may also have a metallic grid work covering them toprevent the entry of large foreign objects. The height of the dischargeoutlets 28 above the transformer adds to the safety of the installation;however, baflles may be strategically disposed in the dome to preventsticks and other foreign objects that may be inserted through the grillwork from coming into contact with dangerous potentials. Or, as analternative, the grid Work may be protected by a bafile. If thetransformer-vault installation 10 is also associated with streetlighting, an electric light pole 32 may be attached, by nut and boltmeans 34, or any other fastening means, to the top of the dome cover 22.Electrical leads 27 and 29 may gain access to the electric light througha suitable opening 35 through the pole 32.

FIG. 2 shows a top view of the transformer-vault com bination 10, shownin FIG. 1. The air openings 26 and 28 may be disposed as shown, or theopenings 28 may be located on sides 36 and 38 of the dome cover 22instead of sides 40 and 42. Further, more or less air outlets 26 and 28may be utilized, depending upon the desired quantity of air flow.

The arrangement shown in FIGS. 1 and 2 also protects the transformer 18from possible damage when vehicles accidentally strike the dome cover22.

When the transformer-vault combination 10 is to be associated withstreet lighting, it is possible to make use of the electrical light polein a manner that provides very efficient air circulation and addedsafety from foreign objects being inserted into the enclosure 12. Thisembodiment of the invention is illustrated in FIGS. 3 and 4, with likereference numerals indicating like components.

More specifically, by utilizing an electric light pole 50 having a largelongitudinal opening 52 therein, a very strong chimney effect isproduced which eliminates the necessity of the air discharge openings 28shown in FIGS. 1 land 2. The heated air will rise through thelongitudinal opening 52 in the electric light pole 50, and may bedischarged through suitable openings near the top of the pole. FIG.shows a perspective view of this type of installation, with airdischarge openings being shown at 54, just below an electric light 60and enclosure 63.

The upper surface 61 of electric light enclosure 63 may be reflectorizedin order to distribute the light to the street below. The sides ofenclosure 63 may also be strategically reflectorized to producedifferent light intensities on the street side as compared to the curbside.

Thus, the air inlet ducts 30 safely divert foreign ob jects placedthrough openings 26 from coming into contact with the transformer 18 andits associated leads and bushings, and the air discharge openings arehigh enough above ground level to be completely safe from foreignobjects. a

To illustrate the effectiveness of the cooling, tests were made using a75 kva. transformer disposed in a subway type enclosure or vault. Themaximum rated winding temperature, ambient plus temperature rise of thetrans former windings was 95 C., and the transformer loads which wouldproduce a maximum winding temperature of 95 C. for different types ofventilation were noted. With a completely closed cover, the 75 kva.transformer had to be derated 18% in order to not exceed the 95 C.

with the air being discharged through a hollow electric light pole. The75 kva. transformer operated without any derating and without exceedingthe 95 C. maximum winding temperature.

FIG. 6 is a graph, with time in hours and days being plotted on theabscissa, and temperature in degrees C. being plotted on the ordinate,showing curves of how the transfarmer winding temperature andtransformer oil temperature varied over a three-day period. Thetransformer was ventilated in accordance with the principles disclosedherein. Dotted curve 68 is the winding temperature, and the dot-dashcurve 70 is the transformer oil temperature. It can be seen from thegraph in FIG. 6, that With the transformer at 100% load, the windingtemperature 60 did not exceed the maximum temperature rise line locatedat C.

In summary, a new and improved ventilating system for subway or vaultmounted transformers has been disclosed which not only improves the aircirculation efficiency, but provides a safer, less hazardousinstallation. Transformers may be disposed in underground enclosures,utilizing the teachings of this invention, without derating thetransformers, and when the transformer-vault combination is associatedwith electric street lighting, an

efficient, safe, esthetically pleasing installation can be provided.

Since numerous changes may be made in the abovedescribed apparatus anddifferent embodiments of the invention may be made without departingfrom the spirit thereof, it is intended that all matter contained in theforegoing description or shown in the accompanying drawings shall beinterpreted as illustrative, and not in a limiting sense.

I claim as my invention:

1. In combination, an enclosure; electrical inductive apparatus disposedwithin said enclosure; a cover having a sloping side portion forming asubstantially dome shape, with its side portion sloping inwardly fromthe bottom portion of said cover to its top portion; said cover beingdisposed over said enclosure; said cover having at least one openingdisposed near its top portion, and at least one opening disposed nearits bottom portion, with said at least one opening disposed near itsbottom portion being disposed in the side portion of said cover; andduct means extending downwardly from said at least one opening near thebottom portion of said cover to the lower portion of said enclosure;said electrical inductive apparatus heating the surrounding air whenenergized and starting air circulation, with the air heated by saidinductive apparatus rising and being discharged through said at leastone open-ing near the top portion of said cover and air being drawn intothe enclosure through said at least 'one opening near the bottom portionof said cover through said duct means to the lower portion of saidenclosure.

2. The combination of claim 1 wherein said an enclosure is disposed atleast partially below ground level; and including a pole having alongitudinal opening therein; said pole being disposed on the top ofsaid cover.

3. The combination of claim 1 including an electric light pole andassociated electric light; said electric light pole having alongitudinal opening therein and being dis posed upon the top of saidcover; the electrical connection between said electrical inductiveapparatus and said electric light being through the opening in saidelectric light pole.

4. In combination, an enclosure; an electrical transformer disposedwithin said enclosure; a cover having a sloping side portion forming asubstantially dome shape with a substantially flat top portion; thesides of said cover sloping inwardly from the bottom portion of saidcover to its top port-ion; said cover being disposed over saidenclosure; said cover having an opening in its top portion; said coverhaving at least one opening disposed in said side portion near itsbottom portion; duct means extending downwardly from said at least oneopening in the side portion of said cover to the lower portion of saidenclosure; a pole having a longitudinal opening therein and beingdisposed on said cover with the opening in the top of said covercoinciding with the opening in said pole; the heating of saidtransformer when energized starting air circulation, with the air in theenclosure heated by said transformer rising up through the opening insaid pole, and air being drawn in through the bottom openings of saidcover through said duct means to the lower portion of said enclosure.

5. The combination of claim 4 including an electric light disposed onsaid pole; the electrical connections be- 6 tween said transformer andsaid electric light being completed through the longitudinal opening insaid pole.

6. The combination of claim 5 wherein said enclosure is disposed atleast partially below ground level.

References Cited by the Examiner UNITED STATES PATENTS 322,018 7/1885Smith et al 174-16 342,552 5/1886 Westinghouse 3369O X 387,123 7/1888Thomson 33659 415,110 11/1889 Johnson 17416 X 424,778 4/1890 Gee 98493,202,815 8/1965 Moore 240-47 X 3,225,224 12/1965 Rydbeck 317-103 XFOREIGN PATENTS 701,486 1/1931 France.

1,165,708 3/1964 Germany.

3,220 2/ 1903 Great Britain.

LEWIS H. MYERS, Primary Examiner.

ROBERT K. SCHAEFER, Examiner.

T. I. KOZMA, Assistant Examiner.

1. IN COMBINATION, AN ENCLOSURE; ELECTRICAL INDUCTIVE APPARATUS DISPOSEDWITHIN SAID ENCLOSURE; A COVER HAVING A SLOPING SIDE PORTION FORMING ASUBSTANTIALLY DOEM SHAPE, WITH ITS SIDE PORTION SLOPING INWARDLY FROMTHE BOTTOM PORTION OF SAID COVER TO ITS TOP PORTION; SAID COVER BEINGDISPOSED OVER SAID ENCLOSURE; SAID COVER HAVING AT LEAST ONE OPENINGDISPOSED NEAR ITS TOP PORTION, AND AT LEAST ONE OPENING DISPOSED NEARITS BOTTOM PORTION, WITH SAID AT LEAST ONE OPENING DISPOSED NEAR ITSBOTTOM PORTION BEING DISPOSED IN THE SIDE PORTION OF SAID COVER; ANDDUCT MEANS EXTENDING DOWNWARDLY FROM SAID AT LEAST ONE OPENING NEAR THEBOTTOM PORTION OF SAID COVER TO THE LOWER PORTION OF SAID ENCLOSURE;SAID ELECTRICAL INDUCTIVE APPARATUS HEATING THE SURROUNDING AIR WHENENERGIZED AND STARTING AIR CIRCULATION, WITH THE AIR HEATED BY SAIDINDUCTIVE APPARATUS RISING AND BEING DISCHARGED THROUGH SAID